2.5 engine build from a bare used bored block, need advice

[aaron78viper]

Hey guys, i have a bored and lightly ported 2.5 block that has been bored out .040. Looking for advice to do port work to turn about 8k on a hydrostream. I would like to be on the edge of pump gas limits here.. Looking for port height specs that will work well for my application, and other parts i should aim to collect for the build. all help is appreciated.

[FORBESAUTO]

Kinda tricky question. The normal 245/260 port map would do ya fine. The exhaust measurement from deck to top of port is 1.550, transfers and boosters is 2.120. I prefer using the degree wheel method because it doesn't matter about how it's decked and you can see a lot more detail with a piston in the hole. Exhaust opens at 95 atdc and transfer boosters at 122.5 atdc. The angles in floors and roofs have have as much to do with rpm power as the durations. The steeper the angles on the booster ports the more rpm and the less the lower rpm, you want just enough bevel on the transfer roofs to not snag the rings and steep angle on sides toward the boosters away from exhaust. The object is to create a narrow intake charge band across from exhaust port going upward toward spark plug and loop back down toward exhaust port. You want very little angle on the exhaust roof also to prevent a strong flow into the floor of the port causing a bad turbulence. The lower ports a very critical also, need to raise them also, the higher the higher and more rpm power. I like the boost port one to be 4.570 and transfer to be 4.065. You also have to cut lower openings in piston skirt to match so while piston is at bdc it doesn't cover the ports. I'm having real good success running exhaust opening at 89 atdc and transfers at 117 atdc and transfers still having slope in roof for the extra low end torque for heavy bass boats, but have to have a really open chest and many intake side mods to work really well. The 260 setup is simple and a common practice.

[FORBESAUTO]

Go ahead and widen exhaust ports to the castings in the block also. You can also widen booster ports in same manner, but loose some velocity. I like to tighten crankcase up some to pick velocity back up when doing this, just depends on how much and far you wanna go with your build. There tricks upon tricks and would use up all the memory space on this site to try list and explain them all in enough detail that would make sense Just remember everything has to work together, the more you get in the more ya gotta get out. Velocity is everything on intake and flow/ volume on exhaust

[dwilfong]

On a light boat like a stream you can get away with some pretty high timing #. The hard part is doing all the cylinders the same. If you are planing on free handing it with the sleeves in the block good luck.
Opening the ex port will pay off if you also raise the boost, finger and transfer timings.
No use to open the finger ports unless the sleeves where removed and the block finger ports where enlarged.
Timed area is king in a two stroke eng.
My timings are higher than a S3000 block and it runs like a champ.
All depends on how much time you want to spend on the port work. That is where the power is at.
Don't try and free hand it you will more than likely just make a mess out of the block.
What do you have now for measurements on the ports from the deck.

[FORBESAUTO]

Yeah, that's why I said it was a tricky question. There is a million and one ways to build a motor that turns no more than 8. I gave him the 260 specs because he mentioned lightly ported ( which I take as chest work being hes asking about port timing) without going into a lot of detail on all kind of mods, he can make great all around power without a lot of other changes and turn 8 with no problem. Now you can make more power by getting more agressive with timing like the 2nd example I gave him which is 124 on intake, 182 exhaust but needs a better chest and tighter cc to make good power under 8 and not sure how much he wants to get into. With the right set up it makes serious power all the way through though, even in my situation of running a rig in tournament load around 2600 lbs. It's all in how much he is willing to get into.

[aaron78viper]

okay, from what I've read, I dont know if the deck is stock height. I am guessing it is stock height.. I want to do port timing as well as reference heights from the deck. if a 260 cut is more than enough i will do that. does anyone have a link to the port specs?

[Go Time]

At +.040, what piston are you thinking about....its gonna be limited

[aaron78viper]

At +.040, what piston are you thinking about....its gonna be limited

a more affordable one of the options most likely. what options would i have?

[dwilfong]

Here you go have at it. 225, 240 sport jet, 245/260 ,300.

[Krazymaan]

Are you going carbs or injection? Either way, you should be able to go higher than 8k with a decent build.

[aaron78viper]

Are you going carbs or injection? Either way, you should be able to go higher than 8k with a decent build.

carbs, i have a set of wh20s i will need to fix up. they sat somewhere for a long time and need to be rebuilt.

[Go Time]

a more affordable one of the options most likely. what options would i have?

Most aftermarket pistons only go to +.030. Wiescos go larger but I'm not a fan of them in the steel sleeve motor.

[FORBESAUTO]

Wisecos probably your only option at a decent price. Have to run them with a min clearance of .005 I would suggest .007-.008. Also make sure you do the heat/cool cylcles (6) before you ever drive it and then run at least 10 easy hours on it after, up to twenty even better but who can do that.

[bigbluechevy454]

A stock port will turn 8k. Without a problem with a small wheel. What are u trying to do? I’ve seen a 200 2.5 on a stream turn 8300 with a 27 Yamaha copy

[aaron78viper]

A stock port will turn 8k. Without a problem with a small wheel. What are u trying to do? I’ve seen a 200 2.5 on a stream turn 8300 with a 27 Yamaha copy

I want a reliable motor that can run 100 in humid weather and more in good conditions.. with the boat I got I should be able to get it.. just want it to be a crisp setup. It's gotta pull hard from 3k and up